Azide-based gas generating compositions for generating gas to inflate an inflatable vehicle occupant protection device have the advantage that they produce non-toxic nitrogen gas during combustion and produce gas at relatively low gas temperatures, in the range of 1100.degree. to 1500.degree. K.
Non-azide based gas generating compositions, in contrast, typically produce gas at temperatures well above the cool-burning azide systems, typically in the range of 2000.degree. to 2500.degree. K, with some approaching 4000.degree. K. While these hot burning systems potentially are thermodynamically efficient, they present heat management problems.
For instance, it may be necessary, because of the high temperatures, to manufacture certain components of the vehicle occupant protection device of more expensive materials that are resistant to the high temperature gas which is generated. In addition, the non-azide based gas generating compositions tend to produce reaction products which may be in a liquid phase at the high temperature and thus may be more difficult to filter.
Various attempts to cool non-azide based gas generating compositions are described in the patent literature. For instance, it has been proposed to add chemical coolants to the compositions. Chemical coolants, however, tend to add to the volume of the gas generating material required without increasing the gas output. This reduces the gas output per volume of gas generating material in an amount dependent upon the amount of coolant added.
Mechanical approaches to cooling the products of combustion of gas generating compositions involve using filters which function as both a heat exchanger and a particulate trap. However, the gas volume output tends to drop dependent upon the heat loss to the filter, especially if the particulate trapping in the filter is highly efficient.